This invention relates to a process for perforating materials by means of a laser beam and is particularly directed to a process for producing a large number of small holes in a metal sheet, particularly a titanium sheet, rendering such sheet particularly applicable for laminar flow control when such sheet is employed as a porous wing skin material on aircraft.
It is known to utilize a laser for the purpose of removing metal from a metallic material. Thus, U.S. Pat. No. 4,411,730 discloses a process for machining nickel-base superalloys wherein a laser is used to remove metal, leaving a recast layer, followed by chemical milling of the recast layer.
U.S. Pat. No. 4,368,080 discloses a method of removing rust from the surface of a metal object by focusing a laser beam upon the rust to heat the rust to evaporation temperature to thereby evaporate the rust.
Laminar flow control requirements for porous wing skin material used on aircraft necessitates a reliable and consistent method of producing millions of extremely fine holes of the order of about 0.003 inch in diameter, in titanium, e.g., 0.025" thick titanium 6Al-4V, sheet employed for this purpose. An electron beam perforator has been partially successful in producing such small holes consistently. A laser hole perforating system for this purpose, however, is far less costly and does not require a vacuum chamber, but obtaining the required hole size, shape and quality have presented problems.
Thus, earlier titanium test samples which were laser drilled showed encouraging results. However, inconsistent tapered hole shape, and the presence of undesirable recast material in and around the drilled holes presented problems.
An object of the present invention is the provision of an improved method for drilling very small holes of uniform size and shape in metal sheet.
Another object is to provide an efficient and rapid process for producing a large number of small uniform holes in a titanium sheet, by means of a laser beam, to permit such sheet to be efficiently employed as a laminar flow control wing skin material on aircraft.
Still another object is to provide a process of the foregoing type for producing a large number of small uniform size holes in a metal sheet, such as a titanium sheet, without depositing recast material or dross in or about the holes.
A still further object is to provide a metal, e.g., titanium, perforated sheet by the process of the invention, having particular utility as an outer wing leading edge of an aircraft, and which provides good laminar flow control efficiency.